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Resistors Combination – Numerical Problem

What is the effective resistance between P and Q in the diagram?

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Asked Malik Ahmed

Answer : 8 ohms

The Two arms have resistances 32 ohm and are in parallel, Their effective resistance is 1 ohms. This is in parallel with the middle arm. So the effective resistance is 8 ohms.

 

OR

The three arms have resistances 32, 1 and 32 respectively and are in parallel. Therefore, taking their reciprocals and adding will give the answer.

An idea shared by Eddie on speed of light barrier

If 24 lights in a series around a circle are wired so that each one switches on as soon as it “sees” the one next to it go on, and switches off as soon as it “sees” the one next to it go off, will the pattern of lights revolve around the circle at a speed close to the speed of light?

A Question from Current Electricity

Pratham asked:

The resistances of 2 bulbs are in the ratio 1:2.if they are joined in series,find the ratio of the energy consumed by the 2 bulbs?

 

Answer:

When connected in series, the same current flows through each of the resistors. Therefore, the energy dissipated is directly proportional to their resistances. That is, the ratio of energy dissipated will nbe same as the ratio of resistances. (1:2)

A numerical problem on Drift velocity

Two conducting wires X and Y of same diameter but different materials are joined in series across a battery . if the number density of electrons in X is twice that in Y . Find the ratio of drift velocity of electrons in the two wires.
(Adithya Singh asked this)

Prepare for Science Quizzes online

We are starting a series of quizzes to enable the students to practice for online quizzes.

Take the sample quiz below for getting an idea on how the quizzes will be coming. If you like it, let us know. Post your reactions as comment to this post. Based on the popularity, we will be adding more such quizzes of different duration and themes.

The Sample Quiz below is of just five questions.

You will get your score and can revise the answers at the end of the quiz.

 

Sample Science Quiz

Question 1

Who encouraged Newton to write his ideas for principia?

A
Einstein
B
Gottfried Wilhelm Leibniz
C
Galileo Galilei
D
Leonardo da Vinci
E
Edmund Halley
Question 2
What is the measure of stellar brightness?
A
Magnitude
B
Albedo
C
Luminous intensity
D
Luminosity
Question 3
What is the reciprocal of impedance?
A
Admittance
B
Conductance
C
Conductivity
D
Permittivity
Question 4
Who formulated the idea " the farther away a galaxy the faster it is moving "?
A
Edwin Hubble
B
Galileo
C
Isaac Newton
D
Kepler
Question 5
Which famous Danish physicist determined the speed of light in 1675?
A
Romer
B
Michaelson
C
Fizeau
D
Foucault
There are 5 questions to complete.
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you are given two nichrome wire of same length and different thickness Which wire will get heated first Give reason.?

You are given two nichrome wire of same length and different thickness Which wire will get heated first Give reason.? Asked Merlin Mary Mathew

Answer:

If the wires are connected one by one to a source, (or connected in parallel to the same source) the one having less resistance (Greater thickness) will get heated up first. This is because, for constant voltage, Heat dissipated is inversely proportional to resistance.

If both are connected in series to a power supply, the one with less thickness will get heated up as same current is flowing through both and then heat generated is directly proportional to resistance.

Alternating Current circuits

John Abraham Asks:

“a circuit has a battery of emf E and internal resistance r.two inductors of inductance L1 and L2 are connected in series to the battery but parallel to each other.what is the current through each inductor in steady state?”

Answer: A pure inductor does not offer any reactance to pure dc. Therefore the only resistance in circuit is the internal resistance. But since the two inductors are in parallel, current through each of them is half the total current in circuit, = E/2r

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